Under the definition used herein, a force-measuring device includes a force-measuring module and an indicator device. The force-measuring module, in turn, includes an electromechanical force-measuring cell serving to determine a force, which functions as a measurement converter in that it converts the input quantity, which is a mechanical force, into an electrical output signal. A special type of multiple force-measuring device exists in the form of a weighing scale with one or more weighing devices, so-called weighing modules. The force-measuring cell is configured in this case as a weighing cell and serves for the mechanical-to-electrical conversion whereby the weight force exerted by a weighing object is converted into an electrical signal. In particular, the weighing cell of a weighing scale serves for the mechanical-to-electrical conversion whereby the weight force exerted by a weighing object is converted into an electrical signal. A force-measuring module or a weighing module as the term is understood here means, respectively, a force-measuring device or a weighing scale without an indicator device.
Larger force-measuring devices often consist of a plurality of force-measuring modules. The force to be measured is in this case distributed by a mechanical device, in particular a measuring plate, over a plurality of force-measuring modules. Each force-measuring module in this arrangement includes a force-measuring cell, by means of which the portion of the force that is imparted to the respective module can be individually determined. The results from the individual force-measuring cells are then passed on to a common output device, where they are combined into an overall result.
Multiple force-measuring devices of this type are used for example in industrial installations for the weighing of the contents of basins, tanks, reactor vessels and the like. Typically in these kinds of applications the weighing modules are configured as high-capacity weighing modules, as so-called tank weighing cells or reactor vessel weighing cells. For each container to be weighed, a plurality of weighing modules are arranged between the feet of the container and the foundation. Thus, each foot of the container rests on a force-measuring module. In order to determine the weight of the container and/or of its contents, the measurement values determined by the force-measuring modules need to be added up, as each measurement value represents a part of the mass. This calculation is in most cases performed in a processor device and/or controller device set up in an adjacent location.
High-capacity force-measuring cells also find application as weighing modules in weighing scales for trucks. Truck scales typically have several measuring plates or weighing plates, each of which rests on a plurality of force-measuring modules. Accordingly, each force-measuring module measures a partial weight of the truck and/or of one or more trailers. The measuring results of the individual force-measuring modules are transmitted to the terminal where they are processed further. The terminal is typically located at some distance from the force-measuring modules, for example in a controller device located as much as several hundred meters away.
According to published application US 2004/0245026 to Brighenti, the terminal, referred to as weighing terminal, is equipped with a display through which the results of the force-measuring device can be released to the outside. In addition, the terminal supplies the force-measuring device with electrical power, with all force-measuring modules being served with electric current from this central power supply. For the transmission of the measurement results and to transmit the electric current, the force-measuring modules are connected to the terminal through various cables. In this connection, the delivery of electrical current and the transmission of the measurement results are channeled through the same cables.
As a cabling arrangement, the individual force-measuring modules are connected by shorter distributor lines to a distribution device, and only the latter has a direct connection through an individual cable, the so-called “home-run” cable, directly to the terminal. The power supply and the transmission of the measurement values are thus merged in the distribution device in order to avoid multiple parallel cables.
The electrical connection of the force-measuring modules through distributor lines and distribution devices increases the risk of installation errors in the setup and in case of repairs leads to a difficult and lengthy process of pinpointing the location of an error. Thus, the requirement exists in particular in larger installations for a simple and efficient way of monitoring the condition of the force-measuring device during operation and installation.
A distribution device is presented in published application DE 101 50 641, in which the condition of the voltage supply, current loops, polarity, and breaks in cables are indicated by means of light-emitting diodes. This device allows a failure diagnosis of the most important malfunctions, but has the disadvantage that this mode of indication does not provide exact quantifiable data about possible functional failures. For example, it is possible for the indication to signal a correct voltage of the power supply, even if the housing or the plug connection of the cables has already been penetrated by moisture. It is therefore possible that corrosion sets in, which in time can lead to the complete destruction of the force-measuring module, although no change can be noticed in the conditions of the voltage supply, loop current, polarity and breakage of a cable.
As a further disadvantage, the monitoring of the optical indication has to take place at the location of the measuring plates. This involves relatively large expenditures for personnel, particularly for large installations and/or in case of inaccessible distribution devices.
It is an objective, therefore, to propose a method for determining the condition of a force-measuring device, a suitable force-measuring device, and a suitable force-measuring module, in particular a weighing device and a weighing module, which allow the condition of the force-measuring device to be determined in a more precise and simple way.